1. Field of the Invention
The present invention relates to an optical subassembly and a method for manufacturing the subassembly.
2. Related Prior Art
Japanese patent application published as JP-H01-207709A has disclosed a transmitting optical subassembly (TOSA). This TOSA comprises a single mode optical fiber, a laser diode (LD), and an optical lens arranged between the optical fiber and the LD. In this TOSA, the single mode optical fiber in a tip thereof positions in a side opposite to the least circle of confusion with respect to a center of a Gaussian mirror surface formed by this lens.
Another Japanese patent application published as JP-2003-241025A has disclosed a TOSA with an optical receptacle configuration that includes a stub.
Such conventional TOSAs generally provide an LD, a lens, a lens cap and a stem. Further, a conventional method for manufacturing the TOSA typically includes a step for setting a distance between the LD and lens where, in an optical system including the LD, the lens and the stub, a maximum optical coupling efficiency therebetween may be achieved, and step for setting a distance between the lens and an optical fiber, which is included within the stub, where a specific output power smaller than the maximum available power is given. That is, the stub is fixed in a point apart from a position where the maximum optical power is obtained; generally, the stub in an end surface thereof is defocused from the lens.
This method mentioned above may bring the following advantages; (1) an alignment tolerance along directions, X and Y, perpendicular to an optical axis may be widened when respective optical elements are fixed to each other because the stub is defocused, and (2) various output power may be obtained only by one type of the TOSA. Thus, after the LD is positioned with respect to the lens such that the maximum optical power is obtained and the stub is adjusted in its position such that the target optical power is obtained, a defocused amount of the stub is widened to expand the tolerance for the misalignment along the optical axis, which brings an advantage in the YAG laser welding for optical elements.
The TOSA carries an optical signal into the optical fiber by mating the receptacle thereof with an optical connector installed in a tip of the optical fiber. However, a fluctuation of the optical power is sometimes observed within the optical fiber. This fluctuation closely relates to a power distribution at an end surface of the stub. The present invention, in view of this phenomenon, provides a TOSA that may reduce the power fluctuation due to an external force applied to the optical connector through the optical fiber, and provides a method for manufacturing the TOSA.